1. Field of the Invention
The present invention relates to a wafer cassette, and more specifically, to a wafer cassette capable of storing semiconductor wafers (hereinafter referred to as “wafers”) having different diameters.
2. Description of the Related Art
Wafer cassettes for transporting wafers are used between processes for semiconductor manufacture. A cassette that is stored with a given number of wafers is used in each manufacturing process. Each of the wafers that are taken out one after another from the wafer cassette is processed as specified. Probers are widely used in a wafer inspection process. A plurality of probers are arranged at given spaces. These probers are used to check the electrical properties of devices that are formed on a wafer.
Normally, a prober comprises a loader chamber and a prober chamber, and examines the electric properties of devices. The loader chamber is provided with a cassette stage portion, a wafer conveyor mechanism, and a pre-alignment mechanism (hereinafter referred to as “sub-chuck”). A wafer cassette that is stored with a plurality of (e.g., 25) wafers placed on the cassette stage portion. The wafer conveyor mechanism transports the wafers one after another from the cassette stage portion. The sub-chuck pre-aligns the wafers that are transported by means of the wafer conveyor mechanism. The prober chamber is provided with a step (hereinafter referred to as “main chuck”), an alignment mechanism, a probe card, and a test head. The main chuck carries each wafer thereon and moves in the X-, Y-, Z-, and θ-directions. The alignment mechanism aligns each wafer in cooperation with the main chuck. The probe card is located over the main chuck. The test head is interposed between the probe card and a tester.
In inspecting the devices, an operator first places the wafer cassette, stored with the wafers, on the cassette stage portion of the loader chamber. Then, the wafer conveyor mechanism takes out the wafers one after another from the wafer cassette, and pre-aligns each wafer on the sub-chuck. The wafer conveyor mechanism moves the wafer onto the main chuck in the prober chamber. In the prober chamber, the main chuck and the alignment mechanism align the wafer. The main chuck indexes the aligned wafer. For each indexing cycle, the prober brings probes of the probe card individually into electrical contact with electrodes of devices formed on the wafer. In this contact state, the devices are checked for electrical properties. After the inspection of the devices on the wafer is finished, the wafer conveyor mechanism in the loader chamber receives the wafer on the main chuck, and returns the wafer to its original location in the wafer cassette. Thereafter, inspection of the subsequent wafers is repeated in the same manner as aforesaid. When inspection of all the wafers in the wafer cassette is finished, the operator replaces the wafer cassette with another one, and repeats the aforesaid inspection for new wafers.
However, development of larger wafers has recently been advanced, and 200-mm wafers are currently being replaced with 300-mm wafers. In semiconductor manufacturing processes including the aforementioned inspection process, the 200- and 300-mm wafers sometimes may be used mixedly. A conventional wafer cassette can only store wafers of one size, thus wafer cassettes of corresponding sizes are used for wafers of different sizes. Therefore, wafer cassettes of a plurality of types having different sizes are used mixedly in semiconductor manufacturing, and their handling is troublesome.
If the diameter of the wafers is 300 mm or more, moreover, it is not only hard but also dangerous for the operator to transport the wafer cassettes. Accordingly, the wafer transportation is expected to be automated by the use of automatic trucks or the like. In this case, the automatic trucks or other transportation apparatuses must handle wafer cassettes of different sizes and involve complicated control operations.
Since the conventional wafer cassettes are molded integrally, moreover, those wafer cassettes whose wafer support portions are damaged must be scrapped.